Basically each Mental World is some sort of dimension (like really, it's a different worlds due to each person having different personalities,
each Mental World is
separated from each other), if I want to put it simply, in combat, Mental World is everything what is surrounded when Mental World Raz is used. Including Sorrow and some sort of "alternate dimension" which also will be a part of Mental World in combat For instance Raz was technically
BFRd in Mental World from one place to another previously and by using Smelling salts it was possible for him to just exit and enter MW again. So if Raz gets sent to the alternate dimension he will just escape mental world and enter it again, since that alternate dimension technically also will be a part of the Mental World. I can basically explain more how Mental Worlds works if needed, cause it's pretty complicated.